Inspiron 640m Erratic Touchpad When Using Power Inverter In Car

Good morning

 

Yesterday I purchased a 150 watt power inverter so that I can use my Inspiron 640m whilst on the move.  I guessed that as laptops usually draw around 60-80w, 150w would be ample.

 

However, when I plug the laptop into the inverter, it charges fine, but the touchpad is erratic.  It is definitely power related because when you unplug the power inverter and use battery power, it goes back to normal.  When you draw more power (i.e. enable WiFi, or turn up the brightness) the touchpad becomes even more erratic.  Conversely, when you draw less power such as dim the brightness or switch to the Power Saver mode, the touchpad is almost usable however still moves and clicks all over the screen.

 

Does anyone have an idea?

 

So far I have removed the Synaptics Drivers and Software and resorted to using the standard Vista "Generic PS/2 Device" drivers but to no avail.

 

I would be very appreciative if someone could help - i'm tearing my hair out thinking of a solution!!!